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Re: The inside dimensions of a rectangular wooden box are 6 inches by 8 in [#permalink]
GreenlightTestPrep wrote:
GeminiHeat wrote:
The inside dimensions of a rectangular wooden box are 6 inches by 8 inches by 10 inches. A cylindrical canister is to be placed inside the box so that it stands upright when the closed box rests on one of its six faces. Of all such canisters that could be used, what is the radius, in inches, of the one that has the maximum volume?

(A) 3

(B) 4

(C) 5

(D) 6

(E) 8

Volume of cylinder = pi(radius²)(height)

There are 3 different ways to position the cylinder (with the base on a different side each time).
You can place the flat BASE of the cylinder on the 6x8 side, on the 6x10 side, or on the 8x10 side

If you place the base on the 6x8 side, then the cylinder will have height 10, and the maximum radius of the cylinder will be 3 (i.e., diameter of 6).
So, the volume of this cylinder will be (pi)(3²)(10), which equals 90(pi)

If you place the base on the 6X10 side, then the cylinder will have height 8, and the maximum radius of the cylinder will be 3 (i.e., diameter of 6).
So, the volume of this cylinder will be (pi)(3²)(8), which equals 72(pi)

If you place the base on the 8x10 side, then the cylinder will have height 6, and the maximum radius of the cylinder will be 4 (i.e., diameter of 8).
So, the volume of this cylinder will be (pi)(4²)(6), which equals 96(pi)

So, the greatest possible volume is 96(pi) and this occurs when the radius is 4

Answer: B

Cheers,
Brent



why can't we place it on the 8*6 with height 10 and volume being 4*4*10 pie?
ie 160pie
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Re: The inside dimensions of a rectangular wooden box are 6 inches by 8 in [#permalink]
shrey09 wrote:
why can't we place it on the 8*6 with height 10 and volume being 4*4*10 pie?
ie 160pie


If we place the flat side of the cylinder on the side that's 8 by 6, the cylinder can't have a radius of 4, because that would mean a diameter of 8, which exceeds the side with length 6.
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